I'm just curious how you think they don't help your ability? i mean, i'm biased too because i am one of those hardcore bumpers, but i feel that just being around people who are that much better than you can only help you get better. Groomers are great, they're fun to go really really fast on, but anyone can do that. You hop onto a bump run and get your shit handed to you, you're going to learn something.
Granted, if all you want to do is stay in the park all day, true, a bump run doesn't hold too much in store for your abilities. But if you'd like to go ski the steepest stuff you can find, drop cliffs, and be able to take on any face on the hill, bumps are a great training ground.